This paper presents the design, development, and experimental validation of a compact quad-port multiple-input multiple-output (MIMO) antenna operating in the millimeter-wave band. The proposed antenna employs circular radiating patches and exhibits an ultra-compact footprint of 7 × 24 × 0.25 mm3. The MIMO design achieved dual-band resonance at 24 GHz and 38 GHz by using modified T-shaped slots in the ground plane. High inter-element isolation exceeding 21 dB is obtained at both operating bands by implementing the slots in the radiating patch and slot in the ground plane. The antenna exhibits peak gains greater than 5.68 dBi with radiation efficiencies of approximately 80% and 88% across the two frequency bands. Furthermore, the envelope correlation coefficient (ECC) remains below 0.018, while the mean effective gain (MEG) exceeds - 6.14 dB, confirming excellent diversity characteristics. In addition, total active reflection coefficient (TARC), channel capacity loss (CCL) and channel capacity (CC) are comprehensively analyzed to assess the antenna's suitability for millimeter-wave MIMO systems. Moreover, the proposed antenna results are validated through equivalent circuit modeling in Advanced Design System (ADS). Practical feasibility is demonstrated through fabrication and experimental measurements. The mechanical flexibility of the antenna is also investigated under bending radii of 20, 40, and 60 mm, showing stable S-parameter performance under deformation. The proposed MIMO antenna's link-margin achieves a data rate of up to 120 Mbps over a communication distance of 120 m at both operating bands. The results of the proposed design demonstrate its strong potential for wearable and high-speed communication applications in next-generation millimeter-wave wireless systems.
Tiwari et al. (2026) studied this question.